The present invention relates to a light modulation device that is employed in for example a projector and in particular relates to a method of manufacturing a light modulation device capable of preventing scattered reflection by reflecting mirrors.
Conventionally, light modulation devices in which light modulation is performed by means of reflecting mirrors are manufactured by mutually connecting together reflecting mirrors with an active element substrate. For example U.S. Pat. No. 441,791 discloses a method of manufacturing a reflecting mirror film and a light modulation device construction employing this reflecting mirror film. According to this reference, a reflective mirror film was manufactured by first of all forming a nitro-cellulose film by spreading on a water surface and lifting this off using a mesh screen then evaporating a metallic film onto it.
However, in this technique, since the reflecting mirror film is not formed on a hard substrate, it is difficult to stick a thin reflecting mirror film in a suitable position on the drive element substrate without physical deformation thereof. If the reflecting mirror film is stuck onto the drive element substrate whilst still in a slack condition, this results in the problem that the quantity of light that is reflected in unwanted directions when the irradiating light is modulated is increased, lowering the contrast between the modulated light and unmodulated light and lowering the utilisation rate of the light.
Also Early Japanese Patent Publication Number H. 6-301066 discloses a technique whereby a mirror array is provided on a glass substrate and, in addition, a resin layer is formed thereon, after which the resin layer is removed from the substrate for each element of the mirror array and an actuator substrate is stuck on. However, the technique disclosed in this reference is a technique wherein a light-reflecting film is stuck onto an actuator array. In order to drive the actuator array, an additional step is necessary for connecting a drive element substrate with the actuator array. This leads to the problem of complicating the process of manufacturing the light modulation device.
In order to avoid these problems it might appear that it would be desirable to manufacture a light modulation device by forming a reflecting mirror on a substrate such as silicon and then removing deformation portions of the reflecting mirror by etching etc. in the form of windows. That is, a light modulation device of a simple construction can be provided without forming the reflecting mirror in a slack configuration. With a light modulation device constructed in this way, the illuminating light that is necessary for display is directed onto the silicon substrate from the windows provided on the substrate, reflected by the reflecting mirror and again emitted from the windows.
However, although such a light modulation device has been devised, the problem arises that scattered reflection of light occurs, causing loss of brightness and/or contrast of the projected image.
With a construction in which windows are provided on the substrate, input and output of light are performed through the windows provided on the substrate so screening and/or scattered reflection of some of the reflected light are produced by the side walls of the windows. In order for handling in the manufacturing process to be carried out easily and safely, a certain film thickness (about 100 xcexcm) is necessary on the substrate so the height of the side walls cannot be made indefinitely low i.e. the substrate cannot be made thin. Since the substrate needs to have a minimum thickness of about 100 xcexcm, in the case of a light modulation device wherein the width of the windows is 50 xcexcm, the side walls of the windows have a height of twice the width. Because of this a considerable proportion of the reflected light is screened and reflected by the side walls at the periphery of the reflecting mirrors, producing a so-called scattered reflecting condition. When an image is displayed using scattered reflected light, the amount of light is insufficient so the brightness of the projected image becomes insufficient and light from other pixels becomes admixed therewith, causing a drop in contrast.
A first object of the present invention is to provide a method of manufacturing a light modulation device whereby light modulation with a high rate of utilisation of the light can be achieved, by providing a step of forming a reflecting mirror such that there is no scattered reflection or sagging.
A second object of the present invention is to provide a projector whereby a projected image can be obtained which is bright with good contrast by providing reflecting mirrors with no scattered reflection and that can easily be deformed without sagging.
The invention for achieving the first object consists in a method of manufacturing a light modulation device comprising:
a) a step of forming a release layer whereby a release layer that produces separation in response to irradiation with incoming light is formed on a heat-resistant substrate having the capability of withstanding heat;
b) a step of forming a reflecting mirror layer whereby a reflecting mirror layer constituted so as to be capable of reflecting light is formed by a piezoelectric material(for example ferroelectric or ordinary dielectric piezoelectric ceramic) on the release layer formed by the release layer forming step;
c) a connection step of electrically connecting (for example the output of the active elements being connected to the second electrode thin-film), corresponding to pixel region units, the reflecting mirror layer that is laminated on the heat-resistant substrate with a active element substrate wherein active elements (for example thin-film transistors) are provided corresponding to pixel regions; and
d) an irradiating separation step whereby said heat-resistant substrate is separated by producing separation in this release layer by irradiating the release layer with light from the side of the heat-resistant substrate.
It should be noted that the reflecting mirror layer could be formed with other layers apart from the piezoelectric layer. A construction in which a plurality of piezoelectric layers are laminated could also be provided.
For example the reflecting mirror layer forming step may comprise a step of forming a first electrode thin-film on the release layer; a step of forming a piezoelectric thin film on the first electrode thin-film; and a step of forming a second electrode thin-film on the piezoelectric thin-film. Preferably the first electrode thin-film is formed by optically reflective material. At least one film of the first electrode thin-film or second electrode thin-film may be formed of optically reflective material.
Also the step of forming the reflective mirror layer may further comprise a step of electrical isolation patterning (forming into squares, polygons or circles such as to effect isolation from the other electrodes), in units of pixel regions, this second electrode thin film and piezoelectric thin film, after the step of forming the second electrode thin film. Specifically, in the step of patterning the second electrode thin film and piezoelectric thin film this second electrode thin film and piezoelectric thin film may be patterned into polygons. Also the second electrode thin film and piezoelectric thin film may be patterned into circles.
Also the connection step may comprise: a step of providing electrodes for connection (for example dyke-shaped electrodes formed by patterning gold may be employed) on one or other of the active element substrate or reflecting mirror layer; and a step of electrically connecting the active element substrate and reflecting mirror layer by means of these connection electrodes. Specifically, in the connection step, the connection electrodes may be formed of gold.
A projector for achieving the second object consists in a projector comprising a light modulation device manufactured by the method of manufacture of the present invention, comprising:
a) an illuminating optical system whereby illuminating light that has been made practically parallel is shone from a direction practically perpendicular to the light modulation device;
b) a screening optical system that optically screens one or other of the reflected light from pixel regions driven by active elements in the light modulation device or pixel regions that are not driven; and
c) a display optical system that forms a display image by imaging the light that has passed through the screening optical system.